Synthesis Of Viologen Derivatives And Their Application As Electrochromic Materials

Electrochromism refers to the phenomenon that the optical properties of electrochromic materials,such as transmittance and reflectivity,change reversibly under applied voltages,and it visually appears as a reversible change in color.Viologens are a type of small organic molecules with bipyridine molecular structure.They have good redox properties and good structural adjustability,and are closely followed by researchers in the field of electrochromism.In this paper,a series of viologen derivatives were synthesized?the molecular structure is as follows?,and the molecular structures of these viologen derivatives were characterized and confirmed by nuclear magnetic resonance spectroscopy(¹H NMR and ¹³C NMR)and mass spectrometry?MS?.In this paper,the author first used UV-vis absorption spectra and cyclic voltammograms?CV?curve to study the optical and electrical properties of the synthesized viologen derivatives.The research results show that these viologen derivatives had good redox properties and absorb in the wavelength range of 200 nm to 800 nm.Subsequently,the gel-type electrochromic devices were prepared by using the viologen derivative as electrochromic active materials,and the electrochromic properties of the corresponding devices were studied.The specific research contents include:Monosubstituted viologen derivatives and their electrochromic devices:the gel-type electrochromic devices ECD 1,ECD 2,and ECD 3 were assembled by using monosubstitu-ted viologen derivatives?TPAV⁺?PF₆^-?,PPV⁺?PF₆^-?,and PCV⁺?PF₆^-??as electrochromic active layers,and the structure of devices was ITO glass/gel electrolyte?which contained monosubstituted viologen derivatives and ferrocene?/ITO glass.The electrochromic properties of the devices were studied.It was found that three monosubstituted viologen derivatives TPAV⁺?PF₆^-?,PPV⁺?PF₆^-?,and PCV⁺?PF₆^-?were all cathode electrochromic materials.Under electrochemical redox conditions,they exhibited reversibly color changes.ECD 1 exhibited reversibly color changes between orange and red;ECD 2 exhibited reversibly color changes between yellow and fuchsia;ECD 3 exhibited reversibly color changes between yellow and tan.Among them,ECD 2 and ECD 3 had high optical contrasts at 563 nm,which were 66.4%and 59.8%,respectively.Compared with the device ECD 3,ECD 1 and ECD 2 had a lower electrochromic driving voltage and better electrochromic cycle stability.Disubstituted viologen derivatives and their electrochromic devices:the gel-type electrochromic devices ECD 4,ECD 5,and ECD 6 were assembled by using disubstituted viologen derivatives(2TPAV²⁺?PF₆^-?₂,2PPV²⁺?PF₆^-?₂,and 2PCV²⁺?PF₆^-?₂)as electrochromic active layers,and the structure of devices was ITO glass/gel electrolyte?which contained disubstituted viologen derivatives and ferrocene?/ITO glass.The electrochromic properties of the devices were studied.It was found that the disubstituted viologen derivativesmaterials.Under electrochemical redox conditions,they exhibited reversibly color changes.ECD 4 exhibited reversibly color changes between fuchsia and red-brown;ECD 5 exhibited reversibly color changes between yellow and orange red;ECD 6 exhibited reversibly color changes between orange and dark green.Compared with the electrochromic device ECD 4,ECD 5 and ECD 6 had a lower electrochromic driving voltage,while having higher optical contrast and higher coloring efficiency at 617 nm.The electrochromic driving voltages of the electrochromic devices ECD 5 and ECD 6 were both-1.2 V,the coloring efficiencies at 617nm were 69 cm²/C and 137 cm²/C,and the optical contrasts were 51.4%and 62.1%,respectively.